The present invention generally relates to ink cartridge units, and more particularly to a cartridge having an internal ink storage bladder of improved design and operating efficiency.
The development of new and improved printing systems has created a corresponding demand for high-efficiency ink cartridges. High efficiency cartridges must be capable of delivering ink in a rapid and continuous manner without interruption. This is especially true with respect to thermal ink jet cartridges which use a collapsible ink storage bladder in combination with a jetting resistor assembly as described in U.S. Pat. No. 4,500,895. The bladder used in these cartridges is designed to retain a substantial amount of ink therein. Likewise, an internal negative pressure is maintained within the bladder so that ink will not drip or "drool" from the jetting orifices when the cartridge is not in use.
When ink is delivered from the cartridge during printer operation, it is correspondingly drawn from the bladder. Because the bladder is air-tight, the withdrawal of ink causes a continuous collapse of the bladder walls inwardly until the bladder is empty. The ink cartridge is then discarded.
Systems of the type described in U.S. Pat. No. 4,500,895 operate in an efficient manner. However, in certain cases, the bladder will collapse improperly, causing an unacceptably high degree of internal bladder back-pressure. If this occurs, the operating systems within the cartridge may not be able to deliver ink against the back-pressure generated by the bladder. As a result, ink delivery from the cartridge is interrupted, causing which is commonly known as a "deprime." A deprime is technically defined as a situation in which excessive bladder back-pressure causes ink to be pulled away from the delivery systems of the cartridge, thereby preventing ink ejection. The interruption of ink delivery as described herein reduces the operating efficiency of the entire printing system.
The present invention involves an improved internal sub-system for ink cartridges which is designed to eliminate the foregoing problems. Specifically, a uniquely-designed ink storage bladder is provided which is characterized by a high degree of reliability as described in detail below.